1. Field of the Invention
The present invention relates to an automatic film loading system of a camera using a film with perforation, such as 35 mm film.
2. Description of the Prior Art
Many kinds of an automatic film loading system have been proposed and used for a 35 mm camera.
Supplying method of the driving power to the film can be classified into two classes. The one is that both the sprocket gear and spool drive the film, and the other is that the spool only drives the film.
In the former system, the sprocket gear hooks the perforations of the film and forward it to wind the spool. The spool has a friction clutch inside thereof, it has been designed such that the rotating speed of the spool is higher than that of the sprocket. Therefore, the difference of the rotating speed between the spool and the sprocket causes slip inside the spool during winding up of the film. In this kind of system, after the film have been caught by the spool, the film is wound up by the rotating force of the spool only. For this reason, in the prior system using the friction clutch, when the torque of the friction clutch is larger than a designed value, required total winding energy is excessively large in comparison with the normal state. Therefore the load of the driving motor is large as a result. It is the problem that the electric consumption increases in comparison with the normal designed operation. Furthermore, as the rotating speed of the spool is fast, sometimes the perforation of the film pass over the teeth of sprocket, and the scratch noise rises. At the worst, the perforations break. On the other hand, in the case where the torque of said friction clutch inside of the spool is excessively low, the film driven by the sprocket is not wound around the spool rightly. As a result, the film is not wound up. The control of the setting of the friction clutch's torque is very difficult on the manufacture in mass production basis, because the natures of the films are different by manufacturers, and the condition of the battery (for instance, voltage) varies.
Furthermore, there is a liability the force to drive the film by the sprocket gear becomes greater than that of the spool. In that case, when the film winding is stopped, if the driving by the spool of the film does not stop instantly, the perforation of the film will break. To prevent such accident, almost of the above-mentioned film loading system provides a friction clutch between the driving motor and the gear train to the sprocket. However, it has the difficulty or troublesome problem to control setting up of the torque of the friction clutch on the manufacturing process, similarly to the above-mentioned friction clutch inside of the spool.
On the other hand, the film loading system which wind up the film by the spool only has one or several hooks on the spool, the film is wound up by being hooked of its perforations to the hook. In this case, therefore, the friction clutch is unnecessary and there is no liability of trouble affected by the friction clutch. In this system, however, the tip of the film must be drawn from a patrone with an accurate length by a user. This is a troublesome matter. For instance, if the film have been drawn longer than the proper length from the patrone, the tip of the film undesirably touches the wall of the spool room, and the film is liable to get out of the hook of the spool, as to the winding system of the spool having one hook therearound. Concerning the winding system of the spool having several hooks there-around, the film is likely to become sagged between several hooks around of the spool. Of course the film is wound around the spool in piles of many layers. Accordingly, care must be taken on positional rotation between the hooks and the layers of wound film. Since drawing out with necessary accurate length of film from the patrone is a difficult matter for layman user, the second type automatic winding system with the spool having the hooks is not always stable in operation. In addition, when plural layers of the wound film pushes a hook which is of a type fixed on the spool, there are apprehension of unstable engagement of the film on the spool. Accordingly, the hook should preferably configurated movable into the spool boss when pressed by the film. Such mechanism, however, is too complex to be mass-produced.